IMO I think too many people get hung up on stated versus actual size.
my 315's were technically 35's but mounted they measured out at about 32-33 can't remember exactly - they had a great stance and provided much better clearance over stock or my buddy's 33's
I now have 37's which measure out at 34.5 on the edge of the tread or 35 on the top.
With the 315's and 4.88 I regained power and mileage on my 3.8, with the 37's there was a drop in power and I'd say pretty considerable drop in gas mileage, it's not much height difference but the overall size makes a difference.
OP you keep saying you don't want to lose mileage but the actual tire size you are wanting contradicts your mileage needs. Also, with 37's you'll need to make sure you have gussets and some power assist, especially if your wife is the primary driver.
I still have the 315's and put them on my 2015 with 3.21 gears. I was surprised how well it still felt, the power drop wasn't too bad and the 5speed makes a big difference as well. I'll do a gear change when I put them on for permanent use but all is back to stock for now.
:twocents: